PUZZLES AND PARADOXES 259 



to undergo a resting stage precisely similar to that of 

 the caterpillar. 



That the contrasts and paradoxes of larval life are 

 many, these pages have already shown. Thus the sala- 

 mander known as the Amblystoma rarely attains to its 

 adult form ; as a larva — the axolotl — it lives and dies, 

 though year after year producing offspring. Not one 

 axolotl in a hundred generations ever assumes the 

 adult form and mode of life- as a land-dweller : it remains 

 to the end of its days a gill-breather, and withal a breather 

 by external giUs. 



In all the other members of the salamander and newt 

 family these external gills are the outward and visible 

 sign of extreme infancy, as in the tadpoles among the 

 frogs. On the other hand, many lowly creatures, Hke 

 the protozoa, are, so to speak, born adults. Having 

 attained the maximum size of their race, they are suddenly, 

 as it were, cleft asunder by an invisible sword, and the 

 two halves become two individuals. There is neither 

 birth nor death, and offspring are denied them. In 

 certain rare cases, as in that of the Pseudis frog, the 

 larva attains a size many times larger than it will ever 

 have when full grown ! 



Sweet liberty is known to many animals only during 

 larval life : in others the reverse obtains. The cater- 

 pillar is tied, so to speak, to its food-plant throughout 

 the whole of its childhood. The longest journey made 

 during this stage is that in search of a place suitable 

 for the dread change which is, after all, to end in such 

 a glorious transfiguration. On the other hand, creatures 

 like the mussel and the oyster have their Wanderjahr very 

 early in life, and settUng down, remain fixed for ever after 

 to the same spot, helplessly anchored; 



